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Mary J Beilby and Virginia A. Shepherd

Modeling current-voltage (I/V) characteristics of salt-tolerant charophyte Lamprothamnium in steady state and at the time of turgor regulation. Mary J Beilby and Virginia A. Shepherd School of Physics, Biophysics, The University of NSW, Sydney Australia. Current – voltage analysis. Membrane

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Mary J Beilby and Virginia A. Shepherd

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  1. Modeling current-voltage (I/V) characteristics of salt-tolerant charophyte Lamprothamnium in steady state and at the time of turgor regulation Mary J Beilby and Virginia A. Shepherd School of Physics, Biophysics, The University of NSW, Sydney Australia

  2. Current–voltageanalysis Membrane current Membrane PD amplifier 4 mA Voltage commands 0 current 200 mV 0 PD 1sec Materials and Methods

  3. Modeling 6 cells in 1/3 seawater: pump state ibackground = gbackground (V – Vbackground) 7 cells in background state

  4. 0.2 SW 77.0 2.0 86.0 140.5 Steady state I/V characteristics in range of salinities Medium Na+ K+ Cl- osmolarity mM mM mM mOsmol.kg-1 0.4 SW 154.0 4.1 172.0 281.0 0.5 SW 175.0 8.0 201.0 536.0 full SW 350.0 16.0 400.0 1072.0 For details see: Beilby and Shepherd, 2001, J. Membrane Biol.181: 77

  5. Hypertonic regulation: from 0.2 SW to 0.4 SW time: 5 min 21 min 41 min 2 hr 34 min 3 hr 30 min

  6. Modeling 0.5 SW, 9 mM K+: cell in K+ state ibackground = gbackground (V – Vbackground)

  7. Hypotonic regulation: 1/3 SW to 1/6 SW cell in K+ state, Cl- current inhibited by La3+ time: (For details see: Beilby and Shepherd, 2001, Aust. J. Plant Physiol.28: 541- 550 ) 3 min 10 min 12 min 15 min 22 min 85 min

  8. Future work Conclusions Transporter for ibackground? H+ channels? Stretch activated channels? • Steady state conductance rises with salinity mainly due to ibackground,Vbackground is not affected by salinity What is the limiting pump conductance? • The proton pump works harder to keep the • membrane PD negative in more saline media Is iirc the detector of hypertonic stress? • Hypertonic regulation turns on iirc before ipump • iirc is carried by K+. Electroneutrality ? • Hypotonic regulation turns on iK independently • of iCl Signal for tonoplast K+ channels to open ? • The increase in [K+]cyt precedes rise in NKPK H+ channels involved in hypotonic regulation? • Vbackground depolarizes and gbackground increases • at the time of hypotonic regulation This presentation can be found on http://www.phys.unsw.edu.au/~mjb/

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